1. Field of the Invention
The present invention relates to a muffler which is located, for example, at the middle of an intake/exhaust ventilation path of an internal combustion engine and which damps intake/exhaust sounds.
2. Background of the Invention
Two types of mufflers, i.e., a side branch type muffler and a resonator type muffler, which will be described hereinafter, are commonly known.
Japanese Patent Application Laid-Open No. 62-126215 discloses the side branch type muffler, as shown in FIG. 14, in which a path body 62 is connected to the middle of an air path pipe 60. An offshoot path 64, whose base end is connected to the air path pipe 60 and whose other end is closed, is bent and formed within the path body 62.
In the conventional side branch type muffler, the frequency of sound waves to be damped (resonance frequency) is determined by the length of the offshoot path 64. In this type of muffler, even if low frequency sounds are to be deadened, a large volume is not needed for the entire muffler compared with the resonator type muffler. Therefore, the side branch type muffler is excellent in this respect. However, when sounds to be deadened are low frequency sounds, the offshoot path must be lengthened due to the muffler having a long, thin configuration. In this case in particular, it is difficult to suitably arrange the muffler within the engine compartment and ability to fit therein is inferior.
In the resonator type muffler, the frequency of sound waves to be damped (resonance frequency) is determined by the volume of a resonance chamber and by the sectional area and the length of a communicating pipe provided in the resonance chamber. With the resonator type muffler, not only can sound waves of the resonance frequency be damped, but sound waves of frequencies in the vicinity of the resonance frequency can be simultaneously damped as well. The resonator type muffler is excellent in this respect. However, there has been a drawback in that the volume of the resonance chamber of the muffler must be made relatively large. Especially when the resonance frequency is in a low frequency range, this drawback becomes marked. It is therefore not easy to install the muffler in a narrow engine compartment.
Because of the above-described circumstances, the special sound characteristics of the internal combustion engine whose sounds are to be deadened and the limitations of the space of the engine room are taken into consideration when selecting an appropriate type of muffler to be mounted to an internal combustion engine. The selection of the muffler is effected on a case-by-case basis.
However, usually sounds generated by an internal combustion engine vary in accordance with the engine speed and encompass a wide range of frequencies. Therefore, simply damping the sounds of only a certain frequency cannot sufficiently deaden the sounds which are generated by the internal combustion engine and which span a wide range of frequencies. This in turn may lead to dissatisfaction with the results of the sound deadening.
Accordingly, in this type of case, a plurality of mufflers, which correspond to the frequencies of sounds for which damping is desired, is connected to the communicating pipe at separate areas so that the sound deadening capacity improves.
However, a large mounting space is necessary to mount a plurality of mufflers. Therefore, it is difficult actually mount mufflers which correspond to sounds of all of the frequencies for which damping is desired.